The present invention pertains to the measuring set for determination of the sagittal depth and the average central curvature of gel contact lenses in the swollen state.
Besides the measurement of refraction of soft contact lenses in their optical zone, it is also important for their application to measure their entire shape. It is suitable, for the rational selection of an optimum lens according to individual pecularities of the patient eye, to ascertain at least the fundamental indices of the shape of the inner arch of lens, i.e. the sagittal depth of lens of the one hand, and the average inner curvature of the central part of lens on the other, that is of that part which exceeds its optical zone and reaches to the eye limbus or the average curvature from the centre up to the diameter of about 10 mm.
In addition to optical methods, a method using the known principle of depth gauge was suggested for this purpose and apparatuses were developed where a metal needle is slowly slid into a lens freely placed on a circular edge of the given diameter by means of an electric motor drive as far as to the contact with lens centre.
The drive is stopped and the inertial motion of needle is braked with the simultaneous indication of needle position on an indicator in the moment of contact by a conductance signal by means of a relay system.
This equipment is rather costly and virtually inaccessible for numerous distributors of gel contact lenses. In addition to this, for the correct selection of contact lens according to the shape of patient eye, more than one shape parameter of lens must be measured, since differences take place, in addition to the size of eye, also in the shape of cornea and the adjacent sclera. Therefore the present invention solves the characterization of a gel contact lens by means of a simple set with one measuring unit serving for measurement of the sagittal depth of lens and the other unit for the average curvature of lens in its central corneal part. Combination of both these units in one apparatus is advantageous above all because the relatively expensive indication electronic equipment serves for both units. The measurement is so rapid that drying of a lens during both measurements is negligible. Consequently, the real values of one and the same lens are measured.
According to the invention, the information about the shape of lens can similarly be attained rapidly and reliably by means of a substantially simple and several times cheaper equipment, while the resolution power of this equipment corresponds to the limits of accuracy given by the nature of thin object of soft material, i.e. of a typical gel contact lens which is in addition to it wetted with water.